Manufacture of tetraethyllead



May 2, 1961 A. MILLER MANUFACTURE OF TETRAETHYLLEAD Filed Feb. 5, 1958 ma lnruov III United States Patent O MANUFACTURE oF TETRAETHYLLEAD Leo A. Miller, Baton Rouge, La., assigner to Ethyl Corpo- This invention relates to the manufacture of organolead compounds. More particularly, the invention relates to an improved and more economical synthesis of tetraalkyllead compounds, particularly tetraethyllead.

Tetraethyllead is conventionally made by the reaction of monosodium leadV alloy weight percent sodium and 90 Weight percent lead) with ethyl chloride. The product of the reaction of these materials is a heterogeneous mixture including a substantial quantity of excess or unreacted lead, sodium chloride, and relatively minor amounts of tetraethyllead (based on the Weight fraction present). This reaction mixture, or reaction mass, is immersed in water, and the tetraethyllead product is rcmoved by steam distillation. This operation concurrently leaches out most of the salt content of the mass. Because the salt solution so-produced is very dilute, the stream is conventionally ditched, thus resulting in an irrevocable loss of sodium chloride.Y The excess lead is separated from the other components and resmelted.

Even under the foregoing circumstances, the above described reaction has enjoyed great commercial success. Nevertheless, considerable potential savings would be achieved by the ability to produce a conjoint product with -the tetraethyllead, and also by the ability to employ a more economical source of the ethyl groups required for the synthesis. One theoretically possible route providing such advantages would be to react diethyl sulfate and sodium lead alloy, as is proposed by Sullivan patent, U.S. 1,611,695. Unfortunately, tests of the Sullivan process show that only a portion of the ethyl groups available are reacted, so that the overall eiciency of the Sullivan process is not as great as the conventional process described above. In other words, in practice vthe potential advantage of the Sullivan process is not realized, especially in that the available ethyl groups are utilized only in part. Accordingly, no particularly effective process has been found heretofore which fully circumvents the need for using ethyl chloride as an ethylating liquid.

An object of the present invention is, therefore, to provide a new and improved process for the production of tetraethyllead. 4More particularly, an object is to provide a process for the synthesis of tetraethyllead wherein ethylene is fed directly to the process. An additional object is to provide a process which. circumvents the limitation inherent in the prior art, viz., that only one of the .ethyl groups, fixed in making diethyl sulfate, is readily Yutilized in formation of tetraethyllead. Even more vcontinuous operation, is referred to in three separate f stages, described below.

In its most general form, the process involves several 2,982,778 Patented May 2, 1961 ICC integrated steps, viz., rst, the fixation of ethylene by absorption, or by sulfation with a recycle stream, here-l after defined, to form a liquid including diethyl sulfate; secondly, the ethylation of lead provided in the form of sodium lead alloy; and third, a metathesis stage wherein a portion of the reaction mixture from the ethylation stage (after removal of tetraethyllead) is treated to provide recoverable sodium sulfate and a stream for recycling to the sulfation stage. The ethylation stage is followed by recovery of the tetraethyllead formed therein, asindicated above.

In the sulfation stage ethylene is reacted with the recycle stream of ethyl hydrogen sulfate to generate diethyl sulfate. Generally, it has been found desirable to contact the reactants at a temperature between about C. to about 150 C. and between a pressure of from about 150 pounds per square inch to about 250 pounds per square inch. This is the only stage ot the Ventire process wherein supra atmospheric pressure is generally employed. The indicated pressure ranges, are, however, surprisingly, only about one-half the pressure normally considered essential to tix ethylene as diethyl sulfate. By reacting ethylene with an already half ethylated compound -to produce a more fully ethylated stream comprising diethyl sulfate, this extremely important advantage is obtained.

The components fed for start up to the ethylation stage include sodium-lead alloy, vthe diethyl sulfate stream from the sulfation stage, and a solvent for vthe tetraethyllead which is inert at reaction conditions. The ethylation reaction is carried out at moderate pressures, atmospheric if desired, and at moderate temperatures, for example at 70 to 80 C. The reaction and product mixture is a heterogeneous system including solid sodium ethyl sulfate, metallic lead, and a solution of tetraethyllead in hexane. This slurry is transferred to a settling operation. The solids are settled and the supernatant solution is drawn olf and delivered to a distillation column, where separation of the tetraethyllead product takes place, the solvent being recycled to the settling step. The residue is then sent to a second extraction operation, wherein the sodium ethyl sulfate compound is separated from the lead solids by leaching with an ethanol stream obtained from the following or metathesis reactionoperation. The sodium ethyl sulfate is thus leached away from the lead solids, which are passed to a smelting' operation for recovery and realloying with sodium t0 form alloy for the ethylation stage.

In the third or metathesis stage, sulfuric acid is reacted with the sodium ethyl sulfate from the extractor, provided in ethanol solution. This converts the sodium ethyl sulfate to ethyl hydrogen sulfate and sodium sulfate. Generally, it is desirable to contact the reactants at a temperature of from about C. to aboutl30 C. An excess of sulfuric acid is knormally provided, and the product of the reaction is a solution of ethyl hydrogen sulfate in sulfuric acid. In addition, solid sodium sulfate is generated and the ethanol solvent is denuded, at least in part of its original sodium ethyl sulfate content.

The invention will be further understood by referring to the following detailed description of the process and to the tlow diagram which illustrates a typical embodiment of this invention. The identity and function ofthe several units of apparatus schematically shown in the ligure will be readily apparent from theY description below. It is also seen from the foregoing outline that a vital feature for efficiency of the overall process is the separation and recovery operations. These are associated with the individual stages, as described below, but further serve to place certain of the process streams in particularly'lit'c'ondition for reaction in the other stages.

"process. "130 through line 31. Hexane and steam 'are taken off overhead, and the two liquids separated by a simple settling technique, hexane and water being immiscible liquids. The hexane is'then recycled to the ethylator1100 asserts volves the addition of ethylene to ethyl hydrogen sulfate, as generally represented fbythe following equation:

The diethyl sulfate-containing stream so-formed Vis then conveyedfthrough a transfer line .20 to a reactor 100 for the reaction of the ethylation stage.

ETHYLATION OPERATION An ethylato'r 100 receives-the diethyl sulfate stream transferred through line 20 fromthe sulfation stage. Also fed to the ethylation reactor 100 is a selective solvent for tetraethyllead which is inert at reaction conditions. Liquid alkane hydrocarbons 'are particularly suitable for this purpose, hexane being a particularly suitable example. Agitation of the charge is started. Sodium lead alloy in the form of thin akes or'in molten form is then charged to the ethylation reactor 100 through line 21. The reaction proceeds accordings to the following:

-Diethyl Alloy Tetra- Sodium ethyl Lead sulfate ethyllead sulfate Itis seen that the reaction system will be a relatively vthin `slurry of solids (lead and sodiumethyl sulfate). When the reaction is well under way, having an average composition usually lapproaching 90p'ercent completion, 'discharge of the slurry is started, through line 29 to a 'settler-'extractor 140. concurrently, the feeds of the refac'tants and solvent 'are adjusted to maintain constant th'e depth of the liquid `in the ethylator 100. In the settler-extractor 140`a'low'er solids rich portion is formed, isurinounted by a supernatant liquid layer comprising solvent, tetraethyllead, and minor amounts -of ethyl sulfate. 'The liquid layer is transferred to a recovery column 130, whereas the major amount of solvent is distilled overtheafd, and returned through a solvent line 22, usually after condensation, tothe ethylation reactor 100. The rec'overy column operation maybe a vacuum distillation, 'but more frequently is a partial pressure operation, such as' a steam distillation. 'The solids bottom layer from the' settler-extractor 140, consistingV principallyv of vsodium vethyl sulfate and lead, is discharged to a second extractor 120. Small `amounts `of unreacted sodium '.lead alloy may also be present. The solids are introduced into the top of the extractor v12.0 through line 24. Ethanol from a metathesis reactor 110 is introduced near the 'bottom of the extractor l120 through line 26. The ethanol dissolves out the sodium ethyl sulfate of the residue or 'sludge and the resulting solution is carried to the 'metathesis stage reactor 110 through line 27. The re- "maining solids .from the 'extractor 120, consisting predominantly of lead, and small amounts of unreacted sodium lead alloy, is passed to a lead recovery operation 160 through line 2'8. In the lead recovery-realloying section, the lead solids are dried, smelted, and 'combined vwith additional lead and sodium to provide alloy for the Steam is introduced into the distillation column through line 22. The tetraethyllead kis Aremoved from -the 'bottom 'of the' distillation 'column 130 and sent to -storage through line/32.

in the reactor 110 through line 27. Simultaneously con- '4 centrated sulfuric acidfor oleum is introduced therein through line 33. The products of the reaction are sodium sulfate and ethyl hydrogen sulfate. The reaction is represented by the following equation:

Sodium ethyl Sul- Ethyl Sodium sulfato furic hydrogen sulfate acid sulfate The components of a reacted mixture are separated, the sodium sulfate solids being thus ajoint product for sale or use in known manner. The ethanol stream vis returned to the extraction operation following the ethylation operation for selective separation of sodium ethyl sulfate. The ethyl hydrogen sulfate, plus sulfuric acid stream is forwarded to the initial or sulfation operation.

Typically, the sodium sulfate solids are iltered from the ethyl hydrogen sulfate, washed with hexane and sent to storage through linet34. The ethyl hydrogen sulfate and some unreacted sulfuric acid are recycled through line 35 to the absorber-reactor 170 ofthe sulfation stage. Ethanol is distilled from the reactor and recycled through line 26 to the extractor 120.

`In addition to continuous ow operations as generally described in the foregoing, the several steps of the process are fully susceptible to batch operation, as described in Example I, following.

Example I 3170 pounds of monosodiumlead alloy, 2120 pounds of diethyl sulfate and 6000 pounds kof rhexane are introduced into the ethylator 100. The reactor is then sealed. The hexane moderates the heat of reaction, and allows the reaction'to proceed at aitemperature of v83 C. After 4 hours, the ethylator 100 is cooledand vented. The contents are discharged, as a slurry, to the settler-extractor 140. The supernatant liquid, which consists tof a solution of tetraethyllead 'in .hexane is passed to the still whereit is distilled with steam under a pressure of 5 pounds per square inch gauge. Ille hexane after settling Vout the water is recycled to the ethylator 100. The bottoms are drawn off to a settling tank, where the supernatant water is drawn olf, and the TEL is sent to storage. At'etraethyllead yield approaching 1000 pounds will be provided. p

The residuefrom thesettler-extractor is conveyed to the extractor 1Z0, where it 'is treated with'2250 pounds of ethanol vat .50 C. and atmospheric pressure to dissolve out the sodium ethyl sulfate. The 1936 pounds of `residual lead is then dried, and delivered to the alloy kettle, where it is combined with 215 pounds of sodium vto produce fresh alloy for the ethylation. I

The ethanol solution of the sodium ethyl sulfate is delivered to the reactor 110 where it is treated with 670 pounds of 99 percent sulfuric acid'at 120 C. andat atmospheric pressure. The sodium ethyl sulfate is there- 'by converted to ethyl-hydrogen sulfate, which is delivered livered tothe ethylator "100`for reaction with fresh sodiurnlead alloy. p y

The followingexampleisthe same 'as the-foregoing example except with respect to the solvents lemployed in the ethylation stage.

Example Il v Example yI is repeated except that benzene is used to tmoderate heat oireaction and to `dissolve` out they tetraethyllead which is formed in the ethylation reaction.

2180 pounds of monosodium-lead alloy, 1415 pounds of diethyl sulfate, and 4000 pounds of hexane are introduced into the ethylator 100 which is -then sealed and the heat moderated at 80 C. for 2 hours. At the end of that time the contents of the ethylator 100 are discharged, as a slurry, to the settler-extractor 140 at a rate of 1900 pounds per hour. 354 pounds per hour of diethyl sulfate and 545 pounds per hour of sodium-lead alloy are introduced into the ethylator 100. Hexane is K introduced into the ethylator 100 at a rate of 1000 pounds per hour. Under these conditions the liquid level within the ethylator 100 remains constant while reaction contnues. The supernatant liquid after settling, which consists of a solution of tetraethyllead in hexane, is passed to the still 130 from the settler-extractor 140 at a rate of 1167 pounds per hour where it is distilled kwith steam under a pressure of 5 pounds per square inch. Tetraethyllead will be produced at a rate of over about 150 pounds per hour.

The residue from the settler-extractor 140 goes to extractor 120, where it is treated with 375 pounds per hour of alcohol at 35 C. and atmospheric pressure to dissolve out the sodium ethyl sulfate. 324 pounds per hour of residual lead plus some unreacted sodium-lead alloy is delivered to the alloy kettle, where it is combined with 37 pounds per hour of sodium to reproduce fresh alloy for the operation.

The ethanol solution of the sodium-ethyl sulfate is delivered to the reactor 110, where it is treated with 112 pounds per hour of 9-9 percent sulfuric acid at 120 C. and atmospheric pressure. The sodium ethyl sulfate is thereby converted to ethyl hydrogen sulfate, which is delivered to t-he absorber reactor 170. Sodium sulfate is produced at a rate of 144 pounds per hour and is washed and sent to storage.

Ethylene gas at the vrate of 68 pounds per hour is admitted to the absorber reactor `170 where it is sulfated 50 Example IV This example is thesame as the foregoing example except that a mixed solvent, percent by weight isooctane and 50 percent by weight benzene, is used to moderate the heat of reaction in the ethylation stage and to extract the tetraethyllead component from the reaction mixture. The temperature of the ethylation reaction is controlled at 83 C.

' Following the removal of the tetraethyllead from the reaction mixture by the said mixed solvent, ethyl chloride is used to dissolve the sodium ethyl sulfate from the residue. The ethyl chloride is then easily removed by distillation and the sodium ethyl sulfate sent to .the reactor 110 for further reaction with sulfuric acid or oleum.

,in a pressure range of from about 150 pounds per square inch to about 250 pounds per square inch. A highly pre-' ferred temperature is from about 125 C. to about 140,

C. and a highly preferred pressure range is from about 180 pounds per square inch to about 220 pounds per square inch.

The reaction between diethyl sulfate and sodium lead *alloy is generally carried out in an inert solvent which serves to separate the tetraethyllead formed and tomodcrate the heatof reaction. The temperature is generally carried out at a temperature of from about 70 C. to

about C. and at essentially atmospheric pressure.v

A preferred 'temperature range is from about 75 C. tol about 80 C. The composition of the sodium lead alloy is not highly critical. Generally, the weight percent of the sodium contained within the compound is within a range of from about 9 percent to about 1l percent. Monosodium lead alloy, however, is the preferred compound. The sodium lead alloy`can be charged to the ethylator in the form of akes or in molten form.

The solvent for moderating the heat of reaction and for extraction of the tetraethyllead formed can be an inert hydrocarbon solvent which will dissolve tetraethyllead and will not dissolve sodium ethyl sulfate. A mixed solvent is highly preferred under certain circumstances. Examples of such solvents are hexane, isohexane, octane,

isooctane, benzene and mixtures of any of the foregoing.

A preferable solvent for the extraction of sodium ethyl sulfate is any solvent which will dissolve the sodium ethyl sulfate Without dissolving or reacting with the lead or the unreacted sodium lead alloy. Alcohols are a preferred class of solvents but other compounds maybe used therefor. Ethyl alcohol is a preferred solvent of this class even though it reacts somewhat with oleum to form additional diethyl sulfate. Ethyl chloride and ethyl hydrogen sulfate are also highly preferred solvents. Mixed solvents may also be Iused for the extraction of sodium ethyl sulfate.

Reaction betweensulfuric acid and sodium ethyl sulfate is preferably carried out in solution. Thus, the solvent which Iis used for the extraction of the sodium ethyl sulfate from the reaction residue is merely contacted with the sulfuric acid. The reaction is carried out at substantially atmospheric pressure. The reaction is carried out at a temperature of from about 50 C. to about 150 C. A preferred temperature range is from about 80 C. to about 110 C.

Hav-ing fully described t-he invention and the preferable modes of operation, I claim:

l. An integrated process for the manufacture of tetraethyllead comprising forming diethyl sulfate by reacting ethylene and a recycled ethyl hydrogen sulfate, as hereafter defined, then reacting said diethyl sulfate with sodium lead alloy and forming a reaction mixture including tetraethyllead, sodium ethyl sulfate and lead, then contacting said mixture with a rst selective solvent, for the tetraethyllead, and separating a solution of tetraethyllead in said rst solvent, then contacting the so formed residue with a second selective solvent, for the y sodium ethyl sulfate, and separating a solution of sodium ethyl sulfate in said second solvent, then adding sulfuric acid to said solution and reacting with the sodium ethyl sulfate therein and forming sodium sulfate and ethyl hydrogen sulfate, and then recovering the sodium sulfate, and recycling the ethyl hydrogen sulfate.

2. An integrated process for the manufacture of tetraethyllead comprising forming diethyl sulfate by reacting ethylene and a recycled ethyl hydrogen sulfate at a temperature of from about C. to about 150 C. and within a pressure range of about pounds to about 250 pounds per square inch, then reacting said diethyl sulfate with sodium lead alloy at a temperature of from about 70 C. to about 80 C. and at substantially atmospheric pressure and forming thereby a reaction mixture including tetraethyllead, sodium ethyl sulfate, and lead, then contacting said mixture with a irst selective solvent,

memes for :the-tetraethyllead, and separating ,a solution of-tetra ethyllead -in said rst solvent, then contacting the soformed `residue with a second, selective solvent, for the sodium ethyl sulfate, said -solvent being selected from the group consisting of ethyl alcohol, ethyl chloride, 4and ethyl hydrogen sulfate, `and separating ra solution of sodium ethyl sulfate :in Vsaid second solvent, then adding sulfuric acid to said solution vand reacting with -the sodium ethyl sulfate therein at Ia temperature 'of about 100l C. nto `about 130 C., Vand forming sodium sulfate and ethyl hydrogen sulfate and then recovering the sodium sulfate and recycling the ethyl hydrogen sulfate.

3. vThe process of claim 1 further dened'in that the secondselective solvent, for the sodium Vethyl sulfate, is ethyl lhydrogen sulfate.

4. The processof yclaim l further defined in'thatthe second selective solvent, for-the sodium ethyl sulfate, is ethyl alcohol.

5. Theprocess yof claim l further denedin that the second selective solvent, yfor the sodium -ethyl sulfate,iszl

ethyl chloride.

ReferencesCited in the le of this Ypatent UNITED STATES PATENTS Sullivan et a1. ,Dec. 21 11926 Daudt Mar. '4, I19,30

OTHER REFERENCES 

1. AN INTEGRATED PROCESS FOR TEH MANUFACTURE OF TETRAETHYLLEAD COMPRISING FORMING DIETHYL SULFATE BY REACTING ETHYLENE AND A RECYCLED ETHYL HYDROGEN SULFATE, AS HEREAFTER DEFINED, THEN REACTING SAID DIETHYL SULFATE WITH SODIUM LEAD ALLOY AND FORMING A REACTION MIXTURE INCLUDING TETRAETHYLLEAD, SODIUM ETHYL SULFATE AND LEAD, THEN CONTACTING SAID MIXTURE WITH A FIRST SELECTIVE SOLVENT, FOR THE TETRAETHYLLEAD, AND SEPARATING A SOLUTION OF TETRAETHYLLEAD IN SAID FIRST SOLVENT, THEN CONTACTING THE SOFORMED RESIDUE WITH A SECOND SELECTIVE SOLVENT, FOR THE SODIUM ETHYL SULFATE, AND SEPARATING A SOLUTION OF SODIUM ETHYL SULFATE IN SAID SECOND SOLVENT, THEN ADDING SULFURIC ACID TO SAID SOLUTION AND REACTING WITH THE SODIUM ETHYL SULFATE THEREIN AND FORMING SODIUM SULFATE AND ETHYL HYDROGEN SULFATE, AND THEN RECOVERING THE SODIUM SULFATE, AND RECYCLING THE ETHYL HYDROGEN SULFATE. 